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09/09/2005 10:24:51 AM · #1 |
Okay. I am trying to wrap my mind around this and something does not seem right.
I shoot aviation pictures, usually airplanes on approach or taking off from airports, at a distance of say 1/4 of a mile to 1 mile away. I have 3 metering modes on the Nikon and I usually shoot using Center weighted or Spot with good results.
Another guy mentioned he uses a Light meter and meters for incident light.
I can understand if you measure this light at or near the subject, but would you want to measure a "scene" this way.
Your thoughts?
JM |
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09/09/2005 10:49:25 AM · #2 |
Matrix is good for 95% of the time. Sometimes you need to adjust exposure comp. Center weight is good for other 5%.
Nick
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09/09/2005 11:08:28 AM · #3 |
| I use matrix 99% of the time w/ exposure compensation, and spot 1% of the time... with film I used spot 99% of the time. But w/ digital, I can re-shoot faster than setting the spot meter. |
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09/09/2005 12:05:35 PM · #4 |
Regardless of the metering mode, the camera meter measures reflected light, that is, the light reflected off of the subject and into the camera lens. At it's most basic, it assumes that the scene will average to an 18% grey. That's why if you shoot a very dark scene, the camera wants to overexpose and underexpose with a bright scene.
Incident light meters measure incident light, that is, the light falling on the subject from the source. They are not dependent on the amoutn of light the subject reflects. As long as the light hitting the little ball or disk on the incident meter is the same as what is falling on the subject, the exposure will be correct. However, if you were shooting a sunny scene from under a shade tree, you would have to get the meter out into the sun to get the correct exposure.
Clear as mud?
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09/09/2005 12:38:08 PM · #5 |
I do understand how metering works. What I don't get is using in the way I tried to explain. And I don't see the benefit.
If I am taking a picture from quite a distance away, why not use center, spot or matrix. If the subject is fairly close to my position, like a portrait, then incident does make sense. Now on a cloudless or overcast day, when the light is fairly constant, it should not matter. Right?
JM |
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09/09/2005 01:03:47 PM · #6 |
I don't see why an incident meter would be any better than the regular old in-camera ones in the situation you are dealing with. I actually don't see how an incident meter would be practical either.
But regardless, why use a meter at all?
The Ultimate Exposure Computer |
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09/09/2005 01:09:44 PM · #7 |
Originally posted by jmosher:
I do understand how metering works. What I don't get is using in the way I tried to explain. And I don't see the benefit.
If I am taking a picture from quite a distance away, why not use center, spot or matrix. If the subject is fairly close to my position, like a portrait, then incident does make sense. Now on a cloudless or overcast day, when the light is fairly constant, it should not matter. Right?
JM |
Not unless you have a situation that would fool a reflected meter and not a incident one.
Like a small white subject against a dark BG. If you use the camera meter in some type of averaging mode you will probably overexpose the white subject. If you fill the circle on your spotmeter with the white subject, you will underexpose. (This is all assuming that you do not manually dial in exposure compensation)
As long as the light on the incident meter is the same as what is falling on the subject, you don't have to worry as much about such things.
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09/09/2005 01:17:20 PM · #8 |
| incident metering is the most accurate, because it ingnores the relative brightness of the subject. However you must make sure that your subject is receiving the exact same light as the meter. In your situation with the subject being so far away its not the best method. |
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09/09/2005 01:50:06 PM · #9 |
Back in my film days (remember those?) we regularly used incident light metering to expose color transparencies, as this gave much more accurate results than the relatively primitive in-camera metering of the time. For the exposure of positive materials in color there are real benefits to incident metering, especially if you are doing mass production shooting and want to be able to process to batch parameters.
Why? Because your exposure won't change as you zoom in or out, basically. Think of an incident light meter as an adjunct to full-manual shooting in the field, shooting a landscape, say. The scene is a meadow backed by a wall of trees at the forest's edge with a bright blue sky overhead. You take an incident light reading of the light falling on the scene and base your exposure on that. All your darks will be dark, your brights will be bright, all in their correct proportions as the scene displays them. This will be true even if one shot is a wide-angle with a lot of sky and another is a telephoto of the wall of trees and a bit of the meadow. In this second shot, the trees (for example) will be exactly the same value as they were in the wider shot.
Now if, for example, you used the in-camera spot metering mode to set your exposure, it would be reading an entirely different set of values in wide-angle than in telephoto, and the tonal renditions of the 2 images would be potentially very different.
Now, modern matrix-metering modes on digital cameras are very sophisticated and they generally do quite a good job. But even so, the exposure for the wide-angle shot with a lot of bright meadow and a small strip of darker trees will be different (in this mode) from the one offered up when you zoom in so the picture is, say, 2/3 tree and 1/3 meadow.
Does that make sense?
As long as you are shooting in constant light (that is, it's not changing from moment-to-moment as clouds drift across the sun, for example) and as likng as you can meter the same light that is falling on the subject, incident light meters and manual camera settings are a very good way to shoot scenics, especially.
Another area where incident light metering really shines is in doing copies of art, where you are positioning your own lights. Imagine copying a largish painting, and setting up 4 lights: high and low at 45 degrees left, high and low at 45 degrees right. You can use the incident meter to take readings at all 4 corners of the painting and at the center, and realign your lights so all 5 readings are the same, giving you even lighting across the entire canvas. This is almost imnpossible to do precisely by eye alone. Then you give the exact exposure indicated by the meter, and all your tones in the painting are accurately rendered in the out-of-camera image.
Robt.
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